Interferential length and angle measuring devices (also referred to herein as "arrangement") are known from many references. For example, U.S. Pat. No. 4,776,701 (Pettigrew), the entire contents of which are incorporated herein by reference, shows a three-grating interferometer, which in practical applications is reduced to a two grating structure by making one of the gratings reflective. Evaluating the interfering partial beams makes it possible to measure the magnitude and direction of the relative displacement between the two gratings. A phase displacement between the partial beams detected by the detectors is therefore necessary.
German Patent Application DE 23 16 248 A1 (Leitz) discloses an apparatus for measuring displacement that has one transparent and one reflective grating. Three detectors detect the diffraction groups of the zero order and of the positive and negative second order. A clear disclosure of the phase relationships between the light beams detected by the detectors, which do not detect the diffraction groups of the first order, is lacking.